Derivative Activities - Schedule of Additional Information Related to Master Netting Arrangements with Derivative Counterparties (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Derivative [Line Items]
Gross Amounts of Recognized Assets	$ 76,058	$ 33,360
Gross Amounts Offset in the Balance Sheet	(14,250)	(19,706)
Net Amounts of Assets Presented in the Balance Sheet	61,808	13,654
Gross Amounts of Recognized (Liabilities)	(14,250)	(45,929)
Gross Amounts Offset in the Balance Sheet	14,250	19,706
Net Amounts of (Liabilities) Presented in the Balance Sheet	0	(26,223)
Natural gas | Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	29,609	4,240
Gross Amounts Offset in the Balance Sheet	(339)	(1,218)
Net Amounts of Assets Presented in the Balance Sheet	29,270	3,022
Gross Amounts of Recognized (Liabilities)	(339)	(4,790)
Gross Amounts Offset in the Balance Sheet	339	1,218
Net Amounts of (Liabilities) Presented in the Balance Sheet	0	(3,572)
Natural gas | Collars
Derivative [Line Items]
Gross Amounts of Recognized Assets	15,295	16,057
Gross Amounts Offset in the Balance Sheet	(1,447)	(7,671)
Net Amounts of Assets Presented in the Balance Sheet	13,848	8,386
Gross Amounts of Recognized (Liabilities)	(1,447)	(13,345)
Gross Amounts Offset in the Balance Sheet	1,447	7,671
Net Amounts of (Liabilities) Presented in the Balance Sheet	0	(5,674)
Natural gas | Basis Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	8,720	7,686
Gross Amounts Offset in the Balance Sheet	(10,189)	(7,686)
Net Amounts of Assets Presented in the Balance Sheet	(1,469)
Gross Amounts of Recognized (Liabilities)	(10,189)	(3,756)
Gross Amounts Offset in the Balance Sheet	10,189	7,686
Net Amounts of (Liabilities) Presented in the Balance Sheet	0	3,930
Crude oil | Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	15,504	3,567
Gross Amounts Offset in the Balance Sheet	(7)	(1,321)
Net Amounts of Assets Presented in the Balance Sheet	15,497	2,246
Gross Amounts of Recognized (Liabilities)	(7)	(4,711)
Gross Amounts Offset in the Balance Sheet	7	1,321
Net Amounts of (Liabilities) Presented in the Balance Sheet	0	(3,390)
Crude oil | Collars
Derivative [Line Items]
Gross Amounts of Recognized Assets	123
Net Amounts of Assets Presented in the Balance Sheet	123
Gross Amounts of Recognized (Liabilities)		(398)
Net Amounts of (Liabilities) Presented in the Balance Sheet		(398)
Commodity Contract NGLs (C3 - Propane) | Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	1,499	826
Gross Amounts Offset in the Balance Sheet	(2,268)	(826)
Net Amounts of Assets Presented in the Balance Sheet	(769)
Gross Amounts of Recognized (Liabilities)	(2,268)	(18,172)
Gross Amounts Offset in the Balance Sheet	2,268	826
Net Amounts of (Liabilities) Presented in the Balance Sheet	0	(17,346)
Commodity Contract NGLs (NC4 - Normal Butane) | Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	1,942	863
Gross Amounts Offset in the Balance Sheet		(863)
Net Amounts of Assets Presented in the Balance Sheet	1,942
Gross Amounts of Recognized (Liabilities)		(757)
Gross Amounts Offset in the Balance Sheet		863
Net Amounts of (Liabilities) Presented in the Balance Sheet		106
Commodity Contract NGLs (C5 - Natural Gasoline) | Swaps
Derivative [Line Items]
Gross Amounts of Recognized Assets	3,366	121
Gross Amounts Offset in the Balance Sheet		(121)
Net Amounts of Assets Presented in the Balance Sheet	3,366
Gross Amounts Offset in the Balance Sheet		121
Net Amounts of (Liabilities) Presented in the Balance Sheet		$ 121